Remarks on the coarea formula of Fleming and Rishel (Q6139356)

The coarea formula expresses the integral of a function over an open set in Euclidean space in terms of integrals over the level sets of another function. A special case is Fubini's theorem. It was originally published by \textit{W. H. Fleming} and \textit{R. Rishel} [Arch. Math. 11, 218--222 (1960; Zbl 0094.26301)]. In the present article the author provides a modern proof of the formula and discusses some applications.